It is a constant endeavor to find improved techniques for placing identifying marks into high-value documents, such as scripts for proposed motion pictures or television programs, drafts of unpublished books, etc., that are targets for theft or malicious appropriation. The protection that can be offered by these techniques is necessarily limited. For example, if the thief has obtained a copy and chooses to retype the stolen document, there is little or no protection that can be offered.
However, retyping of a lengthy document is an expensive and time consuming action. If the thief is less diligent and attempts to photocopy, fax or otherwise electronically reproduce the stolen document, a good degree of protection can be offered by embedding into each page of a document uniquely identifiable and cryptographically unpredictable markings.
The markings may be made unique to each copy of an original document, or additionally, to each page of each copy. If a stolen copy of a document is retrieved, the unique pattern can be detected by scanning the retrieved page or pages, spatially aligning them with the unmarked original page or pages, and systematically matching the detected pattern of speckles with one of those known to have been embedded into marked copies of the original document.